The top opening of trucks, trailers and containers are often covered by a tarp made of canvas or other material to protect the contents from the elements and prohibit the escape of material out of the container during high winds or high speed movement. In recent years, canvas-type tarp coverings for truck trailers have been rolled and unrolled across the top of the trailer with the use of a bar that runs the length of the trailer. For these types of devices, the covering material is rolled on to (or unrolled from) a cylindrical bar as the bar crawls across the top of the box.
Roll-up tarps generally require a series of bows spanning the width of the top opening of the trailer box or container. The bows and the crossbar running across the centers of the bows support the tarp material over the load contained in the trailer, facilitate movement of the roll bar, and assist placement of the covering material over the opening. However, these prior art bows hinder access to the interior of the box or container. Moreover, the items passing through the opening, such as equipment or rocks, may be relatively large or weighty, damaging the bows and crossbar if contact is made. Even regular exposure to small items, such as grain particles, will cause excessive abrasion of the bows and crossbar by extended contact over time. Hence, in the past, obtaining the advantages of using supporting bows and a crossbar to span the top width of an opening of a trailer box or container has meant that a frame-like obstruction would be present in the opening during loading and unloading of material into the box.
Jespersen, U.S. Pat. No. 5,487,584 attempted to solve this problem by providing a support for a removable covering which can be moved at least partially out of the opening when the covering is removed. However, the support in Jespersen swung outwardly from the trailer's enclosure. When the support members are hanging freely off the side of the trailer the poles are susceptible to bending and eventually become irreplaceably damaged. Further, if the driver wants to pull the trailer without having the trailer's cavity obstructed by the support members, the driver would have to remove the whole system of support members. Accordingly, there is a need for an improved retractable tarp support system.